Mutational Biosynthesis of Hitachimycin Analogs Controlled by the ß-Amino Acid-Selective Adenylation Enzyme HitB.

Hitachimycin is a macrolactam antibiotic with an (S)-ß-phenylalanine (ß-Phe) at the starter position of its polyketide skeleton. (S)-ß-Phe is formed from l-α-phenylalanine by the phenylananine-2,3-aminomutase HitA in the hitachimycin biosynthetic pathway. In this study, we produced new hitachimycin analogs via mutasynthesis by feeding various (S)-ß-Phe analogs to a ΔhitA strain. We obtained six hitachimycin analogs with F at the ortho, meta, or para position and Cl, Br, or a CH3 group at the meta position of the phenyl moiety, as well as two hitachimycin analogs with thienyl substitutions. Furthermore, we carried out a biochemical and structural analysis of HitB, a ß-amino acid-selective adenylation enzyme that introduces (S)-ß-Phe into the hitachimycin biosynthetic pathway. The KM values of the incorporated (S)-ß-Phe analogs and natural (S)-ß-Phe were similar. However, the KM values of unincorporated (S)-ß-Phe analogs with Br and a CH3 group at the ortho or para position of the phenyl moiety were high, indicating that HitB functions as a gatekeeper to select macrolactam starter units during mutasynthesis. The crystal structure of HitB in complex with (S)-ß-3-Br-phenylalanine sulfamoyladenosine (ß-m-Br-Phe-SA) revealed that the bulky meta-Br group is accommodated by the conformational flexibility around Phe328, whose side chain is close to the meta position. The aromatic group of ß-m-Br-Phe-SA is surrounded by hydrophobic and aromatic residues, which appears to confer the conformational flexibility that enables HitB to accommodate the meta-substituted (S)-ß-Phe. The new hitachimycin analogs exhibited different levels of biological activity in HeLa cells and multidrug-sensitive budding yeast, suggesting that they may target different molecules.

Palladium(II)-Catalyzed Synthesis of Dibenzothiophenes from 2-Biphenylyl Disulfides by C-H Functionalization.

The palladium-catalyzed oxidative preparation of dibenzothiophene derivatives from 2-biphenylyl disulfides by C-H functionalization is described herein. This procedure shows a high tolerance toward various functional groups and does not require the further addition of a metal oxidant, a base, or a ligand. Also, the present method was applied to the facile preparation of dibenzoselenophene.

Indium-Catalyzed Reductive Dithioacetalization of Carboxylic Acids with Dithiols: Scope, Limitations, and Application to Oxidative Desulfurization.

In this study an InI3-TMDS (1,1,3,3-tetramethyldisiloxane) reducing system effectively catalyzed the reductive dithioacetalization of a variety of aromatic and aliphatic carboxylic acids with 1,2-ethanedithiol or 1,3-propanedithiol leading to the one-pot preparation of either 1,3-dithiolane derivatives or a 1,3-dithiane derivative. Also, the intact indium catalyst continuously catalyzed the subsequent oxidative desulfurization of an in situ formed 1,3-dithiolane derivative, which led to the preparation of the corresponding aldehydes.